Fuel cell

ABSTRACT

The present invention provides a fuel cell which is capable of improving electric power generation efficiency at a time of high-temperature operation. The fuel cell  10  comprising: a membrane electrode assembly  4;  and a pair of gas separators  7,   8  sandwiching the membrane electrode assembly  4  therebetween, wherein at least one of the gas separator(s)  7  and/or  8  comprises a compact layer(s)  7   c  and/or  8   c  which is capable of preventing permeation of fluid and a porous layer (s)  7   d  and/or  8   d  which allows permeation of fluid, and the porous layer(s)  7   d  and/or  8   d  is impregnated with a water-soluble liquid having higher boiling point than that of water.

TECHNICAL FIELD

The present invention relates to a fuel cell.

BACKGROUND ART

A fuel cell is an apparatus which generates electrochemical reaction ina membrane electrode assembly (hereinafter, referred to as “MEA”.)comprising an electrolyte layer (hereinafter, referred to as“electrolyte membrane”.) and electrodes (an anode catalytic layer and ancathode catalytic layer) arranged on both sides of the electrolytemembrane, and which extracts electrical energy generated by theelectrochemical reaction to outside. Among various fuel cells, solidpolymer electrolyte fuel cell (hereinafter, referred to as “PEFC”.) usedfor domestic cogeneration system, automobiles, and so on can be actuatedin a low temperature region. Because of its energy conversionefficiency, short start-up time, and small-sized and lightweight system,the PEFC has received attention as a power source of a battery car or aportable power supply.

A unit cell of the PEFC comprises a MEA and a pair of current collectorssandwiching the MEA therebetween; the MEA contains a proton conductivepolymer which expresses proton conductance under moisture state. Duringthe operation of PEFC, a hydrogen-based gas (hereinafter, referred to as“hydrogen”.) is supplied to the anode, meanwhile an oxygen-based gas(hereinafter, referred to as “air”.) is supplied to the cathode. Thehydrogen which supplied to the anode is separated into proton andelectron under the action of catalyst contained in the anode's catalyticlayer (hereinafter, referred to as “anode catalytic layer”.) ; theproton generated from the hydrogen reaches a cathode's catalytic layer(hereinafter, referred to as “cathode catalytic layer”.) through ananode catalytic layer and an electrolyte membrane. On the other hand,the electron reaches a cathode catalytic layer through external circuit;by having such a process, it is capable of extracting the electricalenergy. Then, reaction of the proton and the electron reached thecathode catalytic layer with oxygen contained in the air which issupplied to the cathode catalytic layer produces water.

During the operation of PEFC, water distribution in the unit cellsometimes becomes uneven. When water distribution in the unit cellbecomes uneven, in a dried portion where water is little, protonconductive-resistance of the electrolyte membrane increases whereby theelectric power generation efficiency tends to decrease; in a wet portionwhere water is pooled, the excessive water prevents the diffusion ofgas, which tends to lower the electric power generation efficiency. Dueto these reasons, in order to improve electric power generationefficiency, homogenization of water distribution in the unit cell isstrongly demanded.

As an art for the purpose of homogenization of water distribution in theunit cell, for example, Patent document 1 discloses a fuel cell whichcomprises a gas separator having a compact layer and a porous portion,wherein the porous portion of the gas separator except for the porousportion is used for preservation of electrolytic solution. In addition,Patent document 2 discloses a fuel cell system comprising a plate wherea reactant flow path and a liquid flow path are separated by a porousmaterial, wherein pressure difference is given between upstream anddownstream of the reactant flow path, reactant is humidified at theupstream of the reactant flow path and liquid water of the reactant isremoved at the downstream of reactant flow path.

Patent Document 1: Japanese Patent Application Examined No. 8-1803

Patent document 2: International Publication No. WO 2004/51818

DISCLOSURE OF THE INVENTION

Problems to be solved by the Invention

The art of Patent document 1 enables to preserve the electrolyte in theporous portion and to transfer water in the unit cell through porousportion, thereby it is presumably possible to homogenize waterdistribution in the unit cell. However, by the art of Patent document 1,when the fuel cell is operated at high temperature, large quantity ofevaporated water is removed from the unit cell, which makeshomogenization of water distribution in the unit cell difficult. As aresult, the art of Patent document 1 has a problem that the electricpower generation efficiency during high-temperature operation tends tolower. The problem can hardly be solved even by a combination of the artof Patent document 1 and Patent document 2.

Accordingly, an object of the present invention is to provide a fuelcell which can improve electric power generation efficiency duringhigh-temperature operation.

Means for Solving the Problems

In order to solve the above problems, the present invention takes thefollowing means. That is, the fuel cell comprising: a membrane electrodeassembly; and a pair of gas separators sandwiching the membraneelectrode assembly therebetween, wherein at least one of the gasseparators comprises a compact layer which is capable of preventingpermeation of fluid and a porous layer which allows permeation of fluid,and the porous layer is impregnated with a water-soluble liquid havinghigher boiling point than that of water.

In the above invention, a liquid flow path for transporting thewater-soluble liquid having higher boiling point than that of water ispreferably provided in the interface between the compact layer and theporous layer, and/or in the porous layer.

Further, in the above invention, the water-soluble liquid having higherboiling point than that of water is preferably a dilute sulfuric acid.

Effects of the Invention

According to the present invention, since a water-soluble liquid havinghigher boiling point than that of water is impregnated in the porouslayer (s) , it is possible to inhibit water evaporation even duringhigh-temperature operation. That is, according to the invention, evenduring high-temperature operation, it is possible to transfer watercontained in the unit cell through the porous layers, which is capableof homogenizing water distribution in the unit cell. Therefore, theinvention can provide a fuel cell which is possible to improve electricpower generation efficiency during high-temperature operation.

Moreover, in the invention, since a liquid flow path is arranged in theinterface of the compact layer and the porous layer and/or in the porouslayer, impregnating a water-soluble liquid having higher boiling pointthan that of water into the porous layer becomes easier.

Further, in the invention, when the water-soluble liquid having higherboiling point than that of water is a dilute sulfuric acid, in additionto the above effect, poisoning of catalyst contained in the membraneelectrode assembly can be inhibited. Therefore, improvement of electricpower generation efficiency of the fuel cell can be easier.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view showing an embodiment of the fuel cell of thepresent invention.

DESCRIPTION OF THE REFERENCE NUMERALS

1 electrolyte membrane

2 catalytic layer

3 catalytic layer

4 MEA (membrane electrode assembly)

5 gas diffusion layer

6 gas diffusion layer

7 separator (gas separator)

7 a solid flow-path plate

7 b cooling-water path plate

7 c compact layer

7 d porous layer

7 e cooling-water path

7 f liquid flow path

7 g gas flow path

8 separator

8 a solid flow-path plate

8 b cooling-water path plate

8 c compact layer

8 d porous layer

8 e cooling-water path

8 f liquid flow path

8 g gas flow path

9 liquid tank

9 x liquid passage

9 y pump

10 fuel cell

Best Mode for Carrying Out the Invention

In a PEFC, water is produced during its operation. In order to inhibitlowering of proton conductivity, a moisturized reaction gas is suppliedto the unit cell. However, the produced water is movable together withthe reaction gas, for instance, MEA tends to be dried at the vicinity ofreaction gas inlet and the produced water tends to be piled up at thevicinity of reaction gas outlet. When the MEA is dried, protonconductive-resistance increases, so that electric power generationefficiency of PEFC lowers. Moreover, when the produced water is piledup, diffusion of reaction gas becomes disturbed. Hence, occurrencefrequency of the electrochemical reaction lowers, and electric powergeneration efficiency of the PEFC lowers. Because of these, in order toimprove electric power generation efficiency of the PEFC, homogenizationof water distribution in the unit cell is preferred. So as to achievethe purpose, conventionally, fuel cells, wherein water is impregnated inporous portion of the gas separator (hereinafter, referred to as“separator”.) , have been disclosed. Nevertheless, in the conventionalarts, large quantity of water is evaporated during high-temperatureoperation; homogenization of water distribution in the unit cell hasbeen difficult; thereby improvement of electric power generationefficiency during high-temperature operation has been difficult. Inorder to improve electric power generation efficiency duringhigh-temperature operation, inhibiting water evaporation duringhigh-temperature operation seems necessary.

The present invention is developed based on these findings. The mainobject of the present invention is to provide a fuel cell which iscapable of inhibiting water evaporation even during high-temperatureoperation by impregnating the porous portion of the separator withwater-soluble liquid having higher boiling point than that of water, andwhich is capable of improving electric power generation efficiency evenduring high-temperature operation by homogenizing water quantity in theunit cell.

The present invention will now be more specifically described withreference to the drawings. It should be noted that the followingembodiment is an example of the invention; the invention is not limitedby the embodiment shown in the drawings.

FIG. 1 shows an embodiment of a fuel cell 10 of the present invention.In FIG. 1, cross section of the unit cell provided in the fuel cell 10of the invention is schematically shown. As shown in FIG. 1, the fuelcell 10 (hereinafter, it may be referred to as “unit cell 10”.) of thepresent invention comprises: a membrane electrode assembly 4(hereinafter, referred to as “MEA 4”.) including an electrolyte membrane1, a catalytic layer 2 disposed on one surface of the electrolytemembrane 1, and a catalytic layer 3 disposed on the other surface of theelectrolyte membrane 1; a gas diffusion layer 5 arranged on the side ofcatalytic layer 2; a gas diffusion layer 6 arranged on the side ofcatalytic layer 3; a separator 7 arranged outside of the gas diffusionlayer 5; and a separator 8 arranged outside of the gas diffusion layer6. In the electrolyte membrane 1, the catalytic layer 2, and thecatalytic layer 3, polymers having proton conductivity are contained;moreover, in the catalytic layer 2 and the catalytic layer 3, asubstance (hereinafter, referred to as “catalyst”.) which functions as acatalyst for electrochemical reaction occurred during the operation offuel cell 10 is contained. In the fuel cell 10, the separator 7comprises: a compact layer 7 c composed by adhering a cooling-water pathplate 7 b with a solid flow-path plate 7 a made of a compact materialwhich does not allow permeation of fluid; and a porous layer 7 darranged at a concave portion of the compact layer 7 c. Along theinterface of the solid flow-path plate 7 a and the cooling-water pathplate 7 b, cooling-water paths 7 e are formed; along the interface ofthe compact layer 7 c and the porous layer 7 d, a liquid flow path 7 fis formed. Further, in the face of separator 7 opposing to the gasdiffusion layer 5 (including the face of gas diffusion layer 5 side ofthe porous layer 7 d), gas flow paths 7 g for distributing reaction gasare formed. On the other hand, the separator 8 comprises a compact layer8 c which is composed by adhering a cooling-water path plate 8 b with asolid flow-path plate 8 a made of a compact material which does notallow permeation of fluid; and a porous layer 8 d arranged at a concaveportion of the compact layer 8 c. Along the interface of the solidflow-path plate 8 a and the cooling-water path plate 8 b, cooling-waterpaths 8 e are formed; along the interface of the compact layer 8 c andthe porous layer 8 d, a liquid flow path 8 f is formed. Further, in theface of separator 8 opposing to the gas diffusion layer 6 (including theface of gas diffusion layer 6 side of the porous layer 8 d), gas flowpaths 8 g for distributing reaction gas are formed. In addition to theabove structure, the fuel cell 10 of the present invention has a liquidtank 9 to pool a dilute sulfuric acid supplied to the liquid flow path 7f and the liquid flow path 8 f. The liquid tank 9 is connected to theliquid flow path 7 f and the liquid flow path 8 f through liquid passage9 x. To the liquid passage 9 x, a pump 9 y is connected to be used fordelivering the dilute sulfuric acid preserved in the liquid tank 9 tothe liquid passage 9 x.

During the operation of fuel cell 10, for example, moisturized hydrogenis supplied to the catalytic layer 2 through the gas flow paths 7 g andthe gas diffusion layer 5; moisturized air is supplied to the catalyticlayer 3 through the gas flow paths 8 g and the gas diffusion layer 6.The hydrogen supplied to the catalytic layer 2 is separated into aproton and an electron under action of catalyst (e.g. platinum. Same, inbelow.) contained in the catalytic layer 2; the proton produced in thecatalytic layer 2 travels to the catalytic layer 3 through the protonconductive polymer contained in the catalytic layer 2, the electrolytemembrane 1, and the catalytic layer 3. On the other hand, the electronproduced in the catalytic layer 2 travels to the catalytic layer 3 viaexternal circuit. Then, oxygen contained in the air supplied to thecatalytic layer 3 reacts with proton and electron, which travel from thecatalytic layer 2 to the catalytic layer 3, under action of catalystcontained in the catalytic layer 3 to produce water.

As above, during the operation of the fuel cell 10, moisturized hydrogenand air (hereinafter, these may be referred to as “reaction gas” alltogether.) are supplied. Here, it should be noted that the waterproduced during the operation tends to travel together with reaction gastowards the outlet of gas flow paths 7 g and gas flow paths 8 g.Therefore, for example, in the face of unit cell 10 where laminatingdirection of the MEA 4, the gas diffusion layer 5, and so on is definedas the normal line direction, water shortage tends to be caused at theinlet side of the gas flow paths 7 g and the gas flow paths 8 g; watertends to be piled up at the outlet side of the gas flow paths 7 g andthe gas flow paths 8 g or the like. When uneven distribution of water iscaused in the face of the unit cell 10 in this way, protonconductive-resistance tends to increase at the dried portion where watershortage is caused; as a result, electric power generation efficiency islowered. Whereas, at the wet portion where water is piled up, diffusionof reaction gas is disturbed by water; consequently, electric powergeneration efficiency is lowered. Especially, when the fuel cell isoperated at high temperature (e.g., 85° C. or more. Same, in below.),water tends to be evaporated, the area of dried portion expands, whichpresumably tends to lower electric power generation efficiency. Thus, inorder to improve electric power generation efficiency at a time ofhigh-temperature operation, seemingly, homogenization of waterdistribution in the face of the unit cell 10 and reduction of waterevaporation becomes necessary.

From the above point of view, in the fuel cell 10 of the presentinvention, the porous layer 7 d is arranged in the separator 7 and theporous layer 8 d is arranged in the separator 8. By arranging the porouslayers 7 d and 8 d, water existing in the unit cell 10 can go throughfine pores included in these layers so that transporting the water fromthe wet portion to the dried portion becomes possible. As above, byhaving such an embodiment which allows water travels from the wetportion to the dried portion, the fuel cell 10 of the invention enablesto homogenize water distribution in the face of the unit cell 10. Inaddition to the above structure, by supplying the dilute sulfuric acidto the liquid flow paths 7 f and 8 f through the liquid passage 9 x, thefuel cell 10 of the invention has a configuration where dilute sulfuricacid is held in many pores provided in both of the porous layer 7 d andthe porous layer 8 d. It should be noted that saturated vapor pressureof water at 30° C. is 4.25 kPa; whereas saturated vapor pressure ofdilute sulfuric acid (60%) at 30° C. is 0.721 kPa and saturated vaporpressure of dilute sulfuric acid (80%) at 30° C. is 0.024 kPa. So, whendilute sulfuric acid is held in the pores of the porous layers 7 d and 8d (impregnating the porous layers 7 d and 8 d with dilute sulfuric acid), compared with the case where water is not mixed with dilute sulfuricacid, saturated vapor pressure of water mixed with dilute sulfuric acidcan be lowered. Thus, by impregnating the porous layers 7 d and 8 d withdilute sulfuric acid, it is possible to suppress water evaporationduring high-temperature operation. Namely, according to the fuel cell 10in which the porous layers 7 d and 8 d are impregnated with dilutesulfuric acid, even during high-temperature operation, it is possible totransport the water, which has been suppressed evaporation, to the poresof the porous layers 7 d and 8 d. Therefore, such an embodiment allowshomogenization of water distribution in the face of the unit cell 10even during high-temperature operation. As a consequent, by impregnatingthe porous layer 7 d of separator 7 and the porous layer 8 d ofseparator 8 with dilute sulfuric acid, the present invention providesthe fuel cell 10 which is capable of improving electric power generationefficiency even during high-temperature operation.

Hence, according to the fuel cell 10 of the invention, suppressing thewater evaporation becomes possible; even if the porous layer 7 d and theporous layer 8 d are impregnated with dilute sulfuric acid, the dilutesulfuric acid and a part of water may still be discharged together withreaction gas to the outside of unit cell 10. When dilute sulfuric acidis discharged to the outside of unit cell 10, amount of the dilutesulfuric acid having been impregnated into the porous layers 7 d and 8 ddecreases which may weaken the effect for suppressing the waterevaporation. So, in the fuel cell 10 of the invention, the liquid flowpath 7 f and the liquid flow path 8 f are connected to the liquid tank 9through liquid passage 9 x. By this configuration, even if the quantityof dilute sulfuric acid which is impregnated into the porous layers 7 dand 8 d decreases, it is possible to supply dilute sulfuric acid fromthe liquid tank 9 through the liquid passage 9 x. As a result, itbecomes possible to maintain the effect for improving electric powergeneration efficiency during high-temperature operation over the longterm.

In the fuel cell 10 of the invention, constructive material of a piping(not shown in the drawings) communicating with the gas flow paths 7 gand another piping (not shown in the drawings) communicating with thegas flow paths 8 g is not specifically limited to; in view of making aconfiguration which is capable of inhibiting corrosion by dilutesulfuric acid, the face which contacts with the fluid may preferably becoated with a known resin. Moreover, constructive material of the liquidpassage 9 x is not specifically limited to, either; in view of having aconfiguration which is capable of inhibiting corrosion by dilutesulfuric acid, the face which contacts with the dilute sulfuric acid maypreferably be coated with a known resin.

Also, in the fuel cell 10 of the present invention, the method to supplydilute sulfuric acid from the liquid tank 9 to the porous layer 7 dand/or the porous layer 8 d through the liquid passage 9 x is notspecifically limited to. An example for supplying dilute sulfuric acidfrom the liquid tank 9 to the porous layer 7 d and the porous layer 8 dmay comprise the step of using the difference between the pressure ofliquid tank 9 and that of the liquid flow path 7 f or the liquid flowpath 8 f. Other than this, a method for supplying dilute sulfuric acidfrom the liquid tank 9 to the porous layer 7 d and/or the porous layer 8d may be carried out by studying the relation between the operation modeof the fuel cell 10 and discharge of the dilute sulfuric acid inadvance, and controlling the performance of the pump 9 y so as the pump9 y to work in conjunction with the operation mode.

In the above description related to the present invention, a fuel cell10 having the liquid flow path 7 f formed along the interface betweenthe compact layer 7 c and the porous layer 7 d and the liquid flow path8 f formed along the interface between the compact layer 8 c and theporous layer 8 d is shown as an example, the fuel cell of the inventionis not limited to the configuration. When the fuel cell of the inventionis provided with a liquid flow path, the area where the liquid flow pathis provided is not limited to the interface between the compact layerand the porous layer; the liquid flow path may be provided in the porouslayer. In addition, the fuel cell of the invention may have aconfiguration which does not have a liquid flow path. However, in viewof making a configuration which is capable of easily charging dilutesulfuric acid to the porous layer, a liquid flow path is preferablyprovided within the configuration.

When the liquid flow path is provided to the fuel cell of the invention,a method for producing separators having the liquid flow paths is notspecifically limited to. As an example thereof, a method for producingseparators to which liquid flow path is formed in the interface betweenthe compact layer and the porous layer, by fitting the compact layer andthe porous layer wherein liquid flow paths are respectively formed in aface of the porous layer opposing to the concave of the compact layerand/or in a concave of the compact layer. Other than this, a method forproducing separators to which liquid flow path is formed in theinterface between the compact layer and the porous layer may be carriedout by fitting the porous layer to the concave of compact layer so asthe gap (i.e. liquid flow path) to be formed between the concave ofcompact layer and the porous layer. Further, a method for producing theseparator having liquid flow paths formed inside the porous layer may becarried out by fitting the compact layer and the porous layer so as anend of the liquid flow path formed inside the porous layer and an end ofthe liquid passage formed in the compact layer to be connected eachother.

Moreover, in the fuel cell 10 of the invention, the porous layer 7 dprovided to the separator 7 may be arranged to exist over thefull-length of the gas flow paths 7 g, it may also be arranged to existin a part of the region of the gas flow paths 7 g. In the same manner,in the fuel cell 10 of the invention, the porous layer 8 d provided tothe separator 8 may be arranged to exist over the full-length of the gasflow paths 8 g, it may be arranged to exist in a part of the region ofthe gas flow paths 8 g.

Further, in the above description related to the invention, anembodiment where the porous layers 7 d and 8 d are impregnated withdilute sulfuric acid is shown; however, the fuel cell of the presentinvention is not restricted to the embodiment. In the invention, theliquid for impregnating the porous layer of separator may be any kind ofwater-soluble liquid having higher boiling point than that of water, itis preferably a liquid which does not cause deterioration of catalyticfunction and catalyst malfunction. In the invention, examples of liquidwhich are capable of impregnating the porous layer of separator include:dilute sulfuric acid such as dilute sulfuric acid (60%) and dilutesulfuric acid (80%) ; and mixed solution of a dilute sulfuric acid withan electrolyte solution obtained by dissolving, in a solvent, a protonconductive polymer which can form an electrolyte membrane.

In the fuel cell 10 of the invention, the proton conductive polymercontained in the electrolyte membrane 1, the catalytic layer 2, and thecatalytic layer 3 is not specifically restricted to, a known protonconductive polymer which is usable for PEFC may be used. In addition, inthe fuel cell 10 in the invention, the catalyst contained in thecatalytic layer 2 and the catalytic layer 3 is not specifically limitedto, a known catalyst which is usable for PEFC may be used. It should benoted that, in the above description related to the present invention,an embodiment where a proton conductive polymer is contained in thecatalytic layer 2 and the catalytic layer 3 is shown; however, the fuelcell of the present invention is not limited to the embodiment, it mayhave the one where the proton conductive polymer is not contained in thecatalytic layer 2 and/or the catalytic layer 3.

Still further, in the fuel cell 10 of the invention, a materialcomposing the compact layers 7 c and 8 c is not specifically limited to,as long as it can prevent permeation of fluid and be usable as amaterial for composing separators of PEFC; a known material can be used.Also, in the fuel cell 10 of the invention, a material composing theporous layers 7 d and 8 d is not specifically limited to, as long as itcan allow permeation of fluid and be usable as a material for composingseparators of PEFC; a known porous material can be used.

Still further, in the above description related to the presentinvention, an embodiment in which a compact layer 7 c composed byadhering a cooling-water path plate 7 b with a solid flow-path plate 7 aand a compact layer 8 c composed by adhering a cooling-water path plate8 b with a solid flow-path plate 8 a is shown; the fuel cell of theinvention is not limited to the configuration. If a compact layer of theabove embodiment can be integrally formed, it is also possible to formaconfiguration provided with compact layers formed as a single member.

Still further, in the above description related to the presentinvention, another embodiment of a fuel cell 10 comprises a separator 7having a porous layer 7 d and a separator 8 having a porous layer 8 d;the fuel cell of the present invention is not limited to theconfiguration. In the fuel cell of the invention, a separator having theporous layer may be disposed at one side of MEA only; that is, it ispossible to make a configuration having a separator, where porous layeris not provided at another side of the MEA, is disposed.

Still further, in the above description related to the presentinvention, an embodiment in which the gas diffusion layers 5 and 6 areprovided is shown; however, the fuel cell of the invention is notlimited to the embodiment; the one in which either one or both of thegas diffusion layers are not provided may be possible. In order toevenly supplying air to the catalytic layer 2, the catalytic layer 3 andso on, an embodiment where gas diffusion layer 5 and the gas diffusionlayer 6 are provided is preferable. When the gas diffusion layers areprovided to the fuel cell of the invention, configuration of this gasdiffusion layer is not specifically restricted to; any kind of gasdiffusion layer which is usable for PEFC can be used.

The above has described the present invention associated with the mostpractical and preferred embodiments thereof. However, the invention isnot limited to the embodiments disclosed in the specification. Thus, theinvention can be appropriately varied as long as the variation is notcontrary to the subject substance and conception of the invention whichcan be read out from the claims and the whole contents of thespecification. It should be understood that fuel cell with such analternation are included in the technical scope of the invention.

INDUSTRIAL APPLICABILITY

The fuel cell of the present invention can improve electric powergeneration efficiency at a time of high-temperature operation, it ispossible to use as a power source of battery car driven under theenvironment of 85° C. or more or as a portable power supply.

1. A fuel cell comprising: a membrane electrode assembly; and a pair ofgas separators sandwiching said membrane electrode assemblytherebetween, wherein at least one of said gas separators comprises acompact layer which is capable of preventing permeation of fluid and aporous layer which allows permeation of fluid, and said porous layer isimpregnated with a water-soluble liquid having higher boiling point thanthat of water.
 2. The fuel cell according to claim 1, wherein a liquidflow path for transporting said water-soluble liquid having higherboiling point than that of water is provided in the interface betweensaid compact layer and said porous layer, and/or in said porous layer.3. The fuel cell according to claim 1, wherein said water-soluble liquidhaving higher boiling point than that of water is a dilute sulfuricacid.